In the internal combustion engines of today as well as mechanisms associated therewith such as automatic transmissions, a substantial amount of copper is employed in the construction thereof. However, some of the most commonly used additives in lubricating oil compositions servicing the internal combustion systems, e.g., gear oils, are highly corrosive to copper. Specifically, among the most effective agents which have been developed for compounding with lubricants to improve extreme pressure and wear properties are sulfur containing organic compounds, for example, sulfurized triisobutylene and sulfurized diisobutylene, sulfurized terpene, sulfurized hydrocarbon oils, vegetable oils, animal oils, xanthate esters, organic polysulfides, particularly polyalkyl polysulfides which contain active sulfur or sulfur compounds. These wear and extreme pressure agents are corrosive to copper. In addition, those hydrocarbon oils derived from high sulfur containing crude oils wherein the sulfurous components are not thoroughly removed in refining are often corrosive to copper.
To solve this problem of copper corrosion, the prior art employs various copper corrosion inhibitors with varying degree of effectiveness. One such class of inhibitors are disclosed in U.S. Pat. Nos. 2,719,125 and 2,719,126 which are directed to copper corrosion inhibited lubricating oil compositions containing as the copper corrosion inhibitor a 1,3,4-thiadiazole polysulfide characterized by the formula: ##EQU3## where R.sup.2 is a hydrocarbon radical (hydrocarbyl) such as alkyl of from 1 to 30 carbons and x is an integer of from 0 to 8. It is interesting to note that the fact that this particular sulfurous material is an effective copper corrosion inhibitor whereas the other aforementioned sulfur (compounds) of antiwear and extreme pressure properties are corrosive to copper, indicates the unpredictability regarding the function of sulfur compounds as copper corrosion inhibiting agents in the lube oil art.